const PROMETHEUS_BASE =
  process.env.PROMETHEUS_URL ?? 'http://learning_ai_common_plat-prometheus-1:9090';

// ── Types ──────────────────────────────────────────────────────────────────

export interface TrendPoint {
  t: number; // unix ms
  v: number;
}

export interface TrendSeries {
  metric: string;
  unit: string;
  points: TrendPoint[];
  latest: number;
  avg: number;
  peak: number;
}

export interface MemoryTrend {
  available: TrendSeries;
  swap: TrendSeries;
}

// ── Internal helpers ────────────────────────────────────────────────────────

function rangeParams(rangeStr: string): { start: number; end: number; step: string } {
  const end = Date.now();
  const days = rangeStr === '30d' ? 30 : 7;
  const start = end - days * 86_400_000;
  const step = days <= 7 ? '1h' : '4h';
  return { start, end, step };
}

async function queryRange(query: string, start: number, end: number, step: string): Promise<TrendPoint[]> {
  const url = new URL(`${PROMETHEUS_BASE}/api/v1/query_range`);
  url.searchParams.set('query', query);
  url.searchParams.set('start', String(Math.floor(start / 1000)));
  url.searchParams.set('end',   String(Math.floor(end   / 1000)));
  url.searchParams.set('step',  step);

  const res = await fetch(url.toString(), {
    signal: AbortSignal.timeout(15_000),
  });
  if (!res.ok) throw new Error(`Prometheus ${res.status}: ${res.statusText}`);

  const body = (await res.json()) as {
    status: string;
    error?: string;
    data?: { result: Array<{ values: [number, string][] }> };
  };
  if (body.status !== 'success') throw new Error(`Prometheus: ${body.error ?? 'unknown error'}`);

  const result = body.data?.result ?? [];
  if (result.length === 0) return [];

  if (result.length === 1) {
    return result[0].values
      .map(([ts, v]) => ({ t: ts * 1000, v: parseFloat(v) }))
      .filter(p => !isNaN(p.v));
  }

  // Multi-series (e.g. per-CPU steal) → average by timestamp
  const byTime = new Map<number, number[]>();
  for (const series of result) {
    for (const [ts, v] of series.values) {
      const ms = ts * 1000;
      const val = parseFloat(v);
      if (!isNaN(val)) {
        const bucket = byTime.get(ms);
        if (bucket) bucket.push(val);
        else byTime.set(ms, [val]);
      }
    }
  }
  return Array.from(byTime.entries())
    .sort(([a], [b]) => a - b)
    .map(([t, vals]) => ({ t, v: vals.reduce((s, x) => s + x, 0) / vals.length }));
}

function summarize(points: TrendPoint[]): Pick<TrendSeries, 'latest' | 'avg' | 'peak'> {
  if (points.length === 0) return { latest: 0, avg: 0, peak: 0 };
  const vals = points.map(p => p.v);
  const latest = vals[vals.length - 1];
  const avg    = vals.reduce((s, v) => s + v, 0) / vals.length;
  const peak   = Math.max(...vals);
  const round1 = (n: number) => Math.round(n * 10) / 10;
  return { latest: round1(latest), avg: round1(avg), peak: round1(peak) };
}

// ── Public trend queries ────────────────────────────────────────────────────

export async function getDiskTrend(range = '7d'): Promise<TrendSeries> {
  const { start, end, step } = rangeParams(range);
  const points = await queryRange(
    '(1 - node_filesystem_avail_bytes{mountpoint="/"} / node_filesystem_size_bytes{mountpoint="/"}) * 100',
    start, end, step,
  );
  return { metric: 'disk', unit: '%', points, ...summarize(points) };
}

export async function getMemoryTrend(range = '7d'): Promise<MemoryTrend> {
  const { start, end, step } = rangeParams(range);
  const [availPts, swapPts] = await Promise.all([
    queryRange('node_memory_MemAvailable_bytes / 1073741824', start, end, step),
    queryRange(
      '(node_memory_SwapTotal_bytes - node_memory_SwapFree_bytes) / 1073741824',
      start, end, step,
    ),
  ]);
  return {
    available: { metric: 'ram_available', unit: 'GB', points: availPts, ...summarize(availPts) },
    swap:      { metric: 'swap_used',     unit: 'GB', points: swapPts,  ...summarize(swapPts)  },
  };
}

export async function getStealTrend(range = '7d'): Promise<TrendSeries> {
  const { start, end, step } = rangeParams(range);
  // avg() across all CPUs so multi-CPU hosts get a single % value
  const points = await queryRange(
    'avg(rate(node_cpu_seconds_total{mode="steal"}[5m])) * 100',
    start, end, step,
  );
  return { metric: 'steal', unit: '%', points, ...summarize(points) };
}

export async function getIoTrend(range = '7d'): Promise<TrendSeries> {
  const { start, end, step } = rangeParams(range);
  // Total VM block write rate in GB/hr (sda = primary disk).
  // cAdvisor does not expose per-container blkio in this setup, so we use
  // the node-exporter metric which covers all processes including invttrdg.
  const points = await queryRange(
    'rate(node_disk_written_bytes_total{device="sda"}[5m]) * 3600 / 1073741824',
    start, end, step,
  );
  return { metric: 'disk_io_write', unit: 'GB/hr', points, ...summarize(points) };
}

// ── Weekly digest summary (used by digest endpoint + cron) ─────────────────

export interface WeeklyDigestData {
  period: { from: string; to: string };
  steal:   { avg: number; peak: number };
  disk:    { latest: number; peak: number };
  ram:     { avg: number; low: number };
  swap:    { avg: number; peak: number };
  io:      { avg: number; peak: number };
}

export async function getWeeklyDigestData(): Promise<WeeklyDigestData> {
  const [diskData, memData, stealData, ioData] = await Promise.all([
    getDiskTrend('7d'),
    getMemoryTrend('7d'),
    getStealTrend('7d'),
    getIoTrend('7d'),
  ]);

  const to   = new Date();
  const from = new Date(to.getTime() - 7 * 86_400_000);

  const ramVals  = memData.available.points.map(p => p.v);
  const swapVals = memData.swap.points.map(p => p.v);

  return {
    period: { from: from.toISOString(), to: to.toISOString() },
    steal: { avg: stealData.avg,                 peak: stealData.peak },
    disk:  { latest: diskData.latest,            peak: diskData.peak },
    ram:   { avg: memData.available.avg, low: ramVals.length ? Math.min(...ramVals) : 0 },
    swap:  { avg: memData.swap.avg,              peak: swapVals.length ? Math.max(...swapVals) : 0 },
    io:    { avg: ioData.avg,   peak: ioData.peak },
  };
}